I have two servers, lets call them A (FreeBSD 6.2) and B (FreeBSD 7.0). They are connected with a single null modem cable. This is so I can access one if it is having a network/firewall issue or the such.

Things seem to be configured properly as I can get into the serial console from my Gentoo laptop using a USB-serial adaptor and minicom. However, I cannot establish a connection from one server to the other with cu or tip. I get the error message

/dev/cuad0: Device Busy
link down

I'm beginning to suspect that I cannot double up the purpose of a single port (eg "dial in" an "dial out") due to the port being locked for inbound communication. Is there any way to hijack it when I need to establish an outbound connection?

I'm beginning to suspect that I cannot double up the purpose of a single port (eg "dial in" an "dial out") due to the port being locked for inbound communication. Is there any way to hijack it when I need to establish an outbound connection?

set the ttyd0 entry to "off" in /etc/ttys on the server you're calling out from; init q; killall getty; you should now be able to tip cuad0. set the ttyd0 entry back to 'on' and 'init q' again when you're done.

I have two servers, lets call them A (FreeBSD 6.2) and B (FreeBSD 7.0). They are connected with a single null modem cable. This is so I can access one if it is having a network/firewall issue or the such.

Note: you will need two separate serial cables to connect both servers, if you want to be able to connect from one to the other as needed. Connect serial port 1 on system A to serial port 2 on system B. Then connect serial port 1 on system B to serial port 2 on system A.

Then configure both systems to use serial port 1 for the serial console. And to use serial port 2 to "dial-out" to the other server.

Otherwise, using a single cable between serial port 1 on both systems, you'll have both systems outputting data to the serial port (ie the serial console is connected to serial port 1), and you won't have anything available to "dial-out" on to the other server.